Preparation of aldol



27, 1.945. y I F R; BALCAR I 2,372,540 PREPARATION 0F ALDoL Filed May 13, 1945 A TTORNEYS l "Patented Mar. 27, 1945 y T" oFF-ics PREPAIm'rIoN oF ALDoL Frederick R. Balear, Stamford, Conn., asslgnor to Air Reduction Company, Incorporated, New York, N. a corporation of New vYork Application May 13, 1943, Serial No. 486,839

" (ci. 2oz-49) 10 Claims.

This invention relates to an improvement in the preparation of aldol and more ,specificallyl to an improved method for the continuous separation of unreacted acetaldehyde from crude aldol.

This application is a continuation-impart of my application Ser. No. 479,772 filed March 19, 1943.

the1 crude aldol.

`There are further disadvantages occurring when both aldehyde and water are removed from If steam at or above atmospheric pressure is used to effect such removal, the

crude aldol is subjected to a higher temperature than is desirable and as a result there may be In the preparation of aldol by the condensation of acetaldehyde according to the reaction 2CH3CHO CHaCHOHCHzCHO it is generally considered better not to attempt to condense all the aldehyde to aldol but instead to allow the reaction to cease while rsubstantial amounts of the acetaldehyde remain unconverted, or in recoverable form. The crude aldal therefore is a mixture containing aldol. recoverable acetaldehyde, and' the condensation catalyst along with water which may have been added with the condensation catalyst or by dilution of the acetaldehyde. e

When the aldol is to be subjected to further chemical reaction, for example as in the hydrogenation of aldol to produce 1,3-butylene glycol which in turn maybe dehydrated to 1,3-'buta diene, the presence of unreacted acetaldehyde is undesirable and its removal becomes'an essential step in such process. The acetaldehyde is undesirable because during the hydrogenation of aldol it will be hydrogenated to ethyl alcohol, thus reducing the over-all economy of the aldol preparation. Furthermore the hydrogenation of the acetaldehyde liberates a considerable amount of heat lwhich is undesirable since it necessitates provision for greater cooling and may at times cause such an undue temperature rise as to cause Y undesirable secondary reactions to take place.

It has been customary heretofore Wherever such removal of acetaldehyde is contemplated to use methods whereby both the water present in the crude aldol as Well as the unchanged acetaldehyde are removed. Such procedure results in the preparationv of highly concentrated aldol which, due to-its tendency toward polymerization, .forms paraldol, a solid havingv a melting point of about 82 C. Where the aldol, s o purified, does not form a solid phase, there results a very viscous solution, presumably of'paraldol dissolved in aldol. Such l.viscous solutions or solids are dicult to handle in the ensuing steps such as hydrogenation, lfor example, and it is usually necessary to add water to the concentrated aldol in order to make it more fluid so that it may be readily pumped as for example intoa continuous hydrogenation apparatus. r

accompanying dehydration of the aldol to form crotonaldehyde in substantial amounts. The crotonaldehyde formed represents a loss of acetaldehyde and results therefore in a decreased yield of aldol from the acetaldehyde. In addition to crotonaldehyde, there is generally a production of high boiling impurities.

' To avoid subjecting the crudealdol to an unduly high temperature, resort is generally had to the removal of the acetaldehyde under reduced pressure. This operation is more costly due to the power requirements for the production of the reducedpressure and has the further v disadvantage that complete and economical rev covery of the low boiling acetaldehyde in such operation is diflicult to achieve.

It is the object of the present invention to avoid the diiiiculties mentioned and to afford a simple,

economical and effective method of separating and recovering acetaldehyde-from crude aldol.

Other objects and advantages of the invention :will be apparent as it is better understood by reference to the following specification and accompanying drawing, illustrating diagrammatically an apparatus suitable the method.

I have discovered that it is possible to remove the unreacted acetaldehyde from crude aldol at normal atmospheric pressures and in such a manner that the aldol is at no time subjected to elevated temperatures sulicient to cause dehydration of the aldol or lformation of other undegas that the resulting steam-gas mixture has a `dew point not higher than the maximum temperature to which the crude aldol is to be subjected.

I have alsodiscovered that side reactions tending to produce crotonaldehyde, resinous products and other undesirable impurities can be avoided by neutralizing the crude aldol to a point between pH ,5.0 and -pH 7.0 and preferably between pH 6.0,y

f and pH 7.0 prior'tostripping.

The application of thismethod. to crude aldol "results in the complete or substantially complete removal of the acetaldehyde with little or `no re` forfthe practice of i The method permits continuous removal of acetaldehyde from crude aldol and is characterized by the use as a stripping agent of l steam diluted with such an'amount of an inert 2- maval of une water contained in There may even be a slight gain in the amount of water in the product prepared according to my invention, over that originally present in the crude aidol. The resuinng amel is a showing no tendency to crystallize at ordinary temperatures or to become so viscous as to imllil' the ease with which it may be pumped or other'- wise handled. It is also free from appreciable amounts of crotonaldehyde and/or highA boilers and is well adapted for hydrogenation to 1,3- butylene glycol with good yields. The-following descriptionwill show in greater detail a method of carrying out my invention: A

Crude aldoi containing unreacted acetaldehyde and water is first neutralized by the addition of a suitable acid, such as sulphuric, hydrochloric aevauo erally not`commercially feasibleto operate at such or `acetic acid,` to a pHv withinfflthevrang'e oi`l5.0`Ur` to '1;0'and is fed through pipe- 2 tothe top of stripping tower 3 which may Ibe a tower packed with ferrules, raschig rings and the like, or a bubblecup column or similar device. Steam is supplied through valved line 4 and measuredby orice 5 and is mixed with the proper amount of an inert gas supplied through valved line 0 and measured by means of orifice 1. Any gas may be used for dilution of the steam provided that it is inert or incapable of reacting with any of the organic materials present and whose physical characteristics would adapt it to the purpose of the invention. Thus'nitrogen, carbon dioxide, natural gas, combustion gases, if free from oxygen, or any similar gases may be employed. The steam-inert gas mixture is fed into the lower end of tower 3 where it passes upward counter-current to the descending vcrude aldol. The stripped aldol leaves thetower through pipe 8 equipped with a liquid seal.

The condensed steam furnishes an amount of heat suiiicient to volatilize all or substantially all of the acetaldehyde, which in admixture with the inert gas and small amountsA of water vapor leave the stripping tower through line 0, passing to alow temperatures.

In order for the steam to heat and vaporize the vacetaldehyde without exceeding the desired temperature of operation, it is essential that the steam-gas mixture be saturated with respect to 'water vapor at the desired operating temperature. The following table indicates the amount of steam required for saturation of 100 cubic feet of nitrogen for various operating temperatures.`

The nitrogen volume-. ismeasured at the .temperature of the mixture.

.3 Operating temp., C.

Lbs. steam required/100 cu. ft. nitrogen. l. 0G l. 83 2. 47 3. 47

, The following examples illustrate the results obtained by operation by this improved method when applied in an apparatus similar to that described above and having a scrubbing tower two and one-half inches in diameter and filled for about eleven feet of its length with one-half inch ceramic ferrules. The absorption tower for recovery of the acetaldehyde was three inches in diameter and was lled with similar terrines for 40 about eleven feet of its length. The examples water-cooled condenser I0 which may be of any suitable construction such as a water jacketed pipe or .pipes or a coil cooled by a suitable bath.

The greater part ofthe water vapor and a portion of the .acetaldehyde is condensed herein and the total liquid and gaseous products issuing from the condenser through-pipe II are fed into the lower portion of absorbing tower I2, which may be a packed tower, bubble-cap column or the like as in the case of stripping tower 3. The use of condenser I0 is not essential to the operaticm of the invention and if desired the gases from stripping towerA 3 may be introduced directly into absorbing tower I2 without being passed through condenser I0.

Water is fed through line I3 into theupper part of the absorbing tower I2 where it passes downward through the tower. The aqueous solution ci acetaldehyde formed in the absorbing tower I2 leaves through pipe Il equipped with a liquid seal The inert gas escapes from the upper part of absorbing tower .I2 through pipe I5, passes for removal of entrained water through separator I0 equipped with water seal I1, then throllzh'line Il into blower I9, and from the blower is returned to scrubbing tower 3 through line 6. After the cycle is in operation, any loss of inert gas from the cycle maybe made up by feeding added inert gas from any suitable supply through valved line 20.

The acetaldehyde-water mixture withdrawn through pipe .I 4 may be further processed by suitshow, the results obtained at two different rates of feed.

Various changes may be made in the details of the apparatus and procedure without departing from the invention or sacrificing the advantages thereof.

--I-elaim:

1. The method of separating acetaldehyde from a mixture containing acetalfiehyde and aldol which comprises subjecting the mixture to the action of steam diluted with sufficient inert gas to afford a dew'point between 60 and-80 C.

2. The method of separating acetaldehyde from a mixture containing acetaldehyde and aldol which comprises subjecting the mixture to the action of steam diluted with suilicient nitrogen to afford a dew point between 60 and 80 C.

3. The method of separating acetaldehyde from a mixture containing acetaldehyde and -aldol which comprises subjecting the mixture to the 0 action of steam diluted with suiiicent carbon dioxide to afford a dew point between 60 C.

4. The method .of separating acetaldehyde from a mixture containing acetaldehyde and aldol which comprises subjecting the mixture to the .and

action of steam diluted with sufiicient natural gas to aiord a dew point between 60 and 80 C.

5. The method of separating acetaldehyde from a mixture containing acetaldehyde and aldol which comprises subjecting the mixture to the action of steam diluted with suiilcient nitrogen water and returning the inert gas with admixed steam for further use in the treatment of the acetaldehyde-aldol mixture.

8. .The method of separating acetaldehyde from a mixture containing acetaldehyde and aldol which comprises ilrst neutralizing the mixture to a pH within therange of 5.0 to '7.0 and subject- C., washing acetaldehyde from the inert gas withv water and returning the inert gas with admixed steam for further use in the treatment of the acetaidehyde-aldol mixture.

7. The method of separating acetaldehyde from a mixture containing acetaldehyde and aldol which comprises subjecting the mixture to the action of steam diluted with sufficient inert gas to aiIord a dew point between 60 and 80 C., washing acet'aldehyde from the inert gas with ing the mixture to the action of steam diluted with suincient carbon dioxide 'to afford a dew point between 60 and 80 C. n

9. The method of separating acetaldehyde from a mixture containing acetaldehyde and aldol which comprises first neutralizing the mixturey to a pH within the range o1 5.0 to '1.0, and subjecting the mixture to the action of steam diluted with suicient inert gas to aior'd a dew. point between 60 and 80 C.

` 10. The `method of separating acetaldehyde from a mixture containing acetaldehyde and aldol which comprises rst neutralizing the mixture to a pH within the range oi' 5.0 to 7.0, and subjecting the mixturev to the action of steam diluted with suiilcient nitrogen to afford a dew point between 60" and 80 C. i

FREDERICK R. 

